Mechanical flaw indenting device



United States Patent 3,474,665 MECHANICAL FLAW INDENTING DEVICE William T. Pruett and William S. Crownover, Huntsville,

Ala., assignors to the United States of America as represented by the Secretary of the Army Filed Sept. 1, 1967, Ser. No. 665,696 Int. Cl. G01n 3/48 U.S. C]. 73-81 5 Claims ABSTRACT OF THE DISCLOSURE A mechanical flaw indenting device including a guide body having a central, axially extending guide bore and an elongated indenter element, which is slidably received for axial movement within the guide bore. The indenter element is formed along its central, vertically extending axis with a T-slot. A cutting tool is received within the flong, longitudinal, leg of the T-slot and a gage block is disposed within the short, transverse, leg of the slot. The lower, cutting end of the tool protrudes below the lower end of the indenter element. The depth of the groove or indentation made in the test specimen will be determined by the selected gage block; and the shape of the indentation will be determined by the shape of the cutting portion of the tool.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to a device for use in testing material toughness, brittleness, etc., and more particularly for evaluating toughness parameters in high strength materials used, for example, in rocket motor cases. These parameters are especially useful in final inspections of rocket motors prior to firing wherein flaws are detected and thereby inspected for comparison with the critical notch toughness, which has been determined by tests with the flaw indenting device. Such flaws, which may be caused by stress, corrosion, weld cracks, metal impurities, bends, dents in handling, low quality of primary design material, etc., must be inspected as to their criticality regarding the safe and successful operation of the rocket motor. Prior art devices include (1) the ground chisel or punch method, (2) standard milling, and (3) electrical discharge machining. Generation of these flaws in test material by the punch method is rather crude, and any parameters obtained thereby are devoid of accuracy. The standard milling method is expensive, complicated and has the rincipal disadvantage that various forms of notches, e.g., an ellipse, are ditlicult and time-consuming to mill. While the electrical discharge machining method gives better control over notch depth and length than the first two prior art methods, there is a lack of shape control. This method is also costly and time-consuming. Thus, the device of the present invention is advantageous over prior are devices due to the extremely accurate control of final length, depth and shape of the notches. Moreover, the same is rapid in operation, inexpensive to construct and use, and is especially useful with accuracy on thin specimen.

SUMMARY OF THE INVENTION The mechanical flow indenting device of this invention comprises a guide block formed with an axial guide passage for receiving and guiding a cutter holder or indenter, when the latter is avially driven. The holder is formed of two parts secured together as a unit, on part having a central, axially extending T-slot formed therein.

, 3,474,665 Patented Oct. 28, 1969 The long leg of the T-slot is adapted for receiving a cutter tool therein, while the short, transverse, leg of the T-slot receives a gage lock or gage bar therein for varying the depth of the groove or indentation. The lower end wall or base of the guide block is formed with an additional guide groove for matingly receiving the shank of a test specimen therein.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, FIGURE 1, a flaw indenting device 1, according to the present invention, is shown engaged on the shank 15 of a test specimen 16. The device includes a guide block 2, formed in two parts 4, 6 and secured together as by threaded means -8 and guide pins 10. An axial passage 12 extends throughout the length of the guide block. Guide block 2 further has a transverse slot 14 formed in its base, the slot having a width to conveniently seat on the shank 15 of a standard test specimen 16. An elongated cutter holding element or indenter 18 is slidably disposed within passage 12 and the same is adapted to be driven in an axial direction by any suitable power means, e.g., a hydraulic press. Cutter holder 18 is formed in two separate parts 20, 22 (FIG. 4). Part 20 has an elongated T-slot 24 (FIGS. 2 and 3) formed therein while part 22 is secured to part 20 as by threaded means 26 and offset guide pins 28. The inner wall of part 22 thus forms one wall of the T-slot. A cutter tool 30 is slidably positioned in the vertically extending or long leg of the T-slot. The cutting portion 32 of the tool may take many different shapes; however, a typical tool which has been found desirable has 60 site angled faces with a ratio of 3 to 1 width to depth. To provide mans for accurately varying the depth of cut or indentation, a gage block 34, selected from a family of gage blocks, is placed in the transverse or short leg of the T-slot. It is apparent that the transverse slot is formed of a width which will allow gage blocks of varying width or thickness to be utilized whereby indentations of varying depths may be made.

In operation, a selected cutter tool is placed in the long leg of the T-slot and a selected gage block is placed in the transverse or short leg of the slot. Element 22 is secured to element 20 thereby maintaining the tool and gage block in their respective slots. The indenter 1 8 is then driven axially of guide block 2 as by a hydraulic press or the like power means. After the indention 40 is made, the specimen is placed in test apparatus to determine the critical notch toughness, brittleness, etc. These test parameters are particularly useful when inspecting flaws in rocket motors and the like hardware.

What is claimed is:

1. A mechanical flaw indenting device comprising: an elongated guide block formed with an axial guide passage, said block having a transverse slot formed in its lower end for seating engagement on the shank of a material specimen; an indenter guide element slidably received in said guide passage; a cutter tool slidably disposed within said indenter guide element, said tool being formed on its lower end for making an indentation in said specimen when saidindenterguide element is-driven axially of said guide passage toward said specimen.

2. A mechanical flaw indenting device as defined in claim 1 wherein said indenter guide element is formed with a vertically extending T-slot, and wherein said cutter tool is received within the long leg of said slot.

3. A mechanical flaw indenting device as defined in claim 2, wherein gage means is received within the transverse, short leg of said slot for gaging the indentation depth of said tool.

4. A mechanical flaw indenting device as defined in claim 3 wherein said gage means are defined by variable width gage blocks.

5. A mechanical fiaw indenting device as defined in claim 3 wherein said indenter guide element is defined by a rectangular block, said last-named block being formed of two parts, one of said parts having the T-slot formed 7 4 therein and the other of said parts being removably secured to said one part so as to form one side wall of "said T-slot, the arrangement thereby allowing interchangeability of cutter tools and gage blocks.

References Cited UNITED STATES PATENTS 1,903,524 4/1933 Webster 7381 2,716,884 9/1955 Rosenberg 7312 2,942,458 6/1960 Kerr 7382 FOREIGN PATENTS 1,162,211 9/1958 France.

RICHARD C. QUEISSER, Primary Examiner C. E. SNEE III, Assistant Examiner 

